Polyvinylidene fluoride (hereinafter, abbreviated as PVDF) is excellent in mechanical strength and chemical resistance and is used as a pipe line material and a lining material for inner surfaces of a storage tank and a reaction container in chemical plants. PVDF is also excellent in weather resistance and thus is used as interior and exterior plastic plates for various architectures and automobiles, a surface protection film for a substrate such as a metal plate, and an insulating material for a member in electric and electronic equipment.
In recent years, PVDF has been drawing attention as a material for a weather resistant film constituting a back sheet of a photovoltaic power generation module (for example, see Patent Document 1). The solar cell module is required to have outdoor durability for a long time, and thus generally has an integrated structure in which a transparent substrate composed of glass or the like, a sealer composed of, for example, a sheet of a thermoplastic resin such as an ethylene vinyl acetate copolymer (EVA), a solar cell as a photovoltaic device, and a back sheet are stacked in this order and laminated by a method such as hot press.
The back sheet for a solar cell is used as the lowermost layer in a solar cell module in order to protect the solar cell and wiring, but is required to have an effect of increasing sunlight reflectivity for the increase of power generation efficiency of the solar cell module in addition to the protection effect. On this account, a conventional solar cell module mainly uses a white sheet, and the PVDF film for a solar cell generally contains a white pigment (for example, see Patent Document 2). Conventionally, in order to increase hiding power of the film, there is also disclosed a back sheet for a solar cell containing a slight amount of a colored inorganic pigment for toning in addition to the white pigment (for example, see Patent Document 3).